Outpay Developer Docs: Payment API, Checkout, and Webhooks

Build an Outpay crypto payment integration with the verified REST API, hosted USDC checkout, idempotency, testing, and signed webhooks.

Who this is for

This section is for developers building a server-side integration against the Outpay public v1 API. If you only need a shareable payment link with no code, see the merchant guide instead.

Checkouts

Create, redirect, read, expire, and reconcile a hosted checkout.

Webhook verification

Verify the raw request body before fulfilling an order.

Idempotency

Retry checkout creation without creating duplicate payment requests.

Production checklist

Review the controls required before a real integration goes live.

The recommended lifecycle

Create an API key with only the scopes your server needs.
Create one checkout per merchant order, with a stable idempotency key derived from your order ID.
Redirect the customer to the returned paymentUrl.
Verify the signed checkout.paid webhook on your server and fulfil the order exactly once.
Poll the checkout or list payments for reconciliation and support tooling — never as your primary fulfilment signal.

Do not trust the redirect

Success and cancellation URLs are customer navigation events, not payment proof. A customer can close the tab, or an attacker can guess the success URL. Fulfil only from a verified webhook or a server-side status read.

API reference — the strict endpoint contract.
Webhooks — event types, signing, and delivery behaviour.
Testing — validate your integration before going live.